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J Appl Physiol 69: 2155-2162, 1990;
8750-7587/90 $5.00
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Journal of Applied Physiology, Vol 69, Issue 6 2155-2162, Copyright © 1990 by American Physiological Society

ARTICLES

In situ characterization of carbonic anhydrase activity in isolated rat lungs

T. A. Heming and A. Bidani
Department of Internal Medicine, University of Texas Medical Branch, Galveston 77550.

Lung carbonic anhydrase (CA) participates directly in plasma CO2-HCO3(-)-H+ reactions. To characterize pulmonary CA activity in situ, CO2 excretion and capillary pH equilibration were examined in isolated saline-perfused rat lungs. Isolated lungs were perfused at 25, 30, and 37 degrees C with solutions containing various concentrations of HCO3- and a CA inhibitor, acetazolamide (ACTZ). Total CO2 excretion was partitioned into those fractions attributable to dissolved CO2, uncatalyzed HCO3- dehydration, and catalyzed HCO3- dehydration. Approximately 60% of the total CO2 excretion at each temperature was attributable to CA-catalyzed HCO3- dehydration. Inhibition of pulmonary CA diminished CO2 excretion and produced significant postcapillary perfusate pH disequilibria, the magnitude and time course of which were dependent on temperature and the extent of CA inhibition. The half time for pH equilibration increased from approximately 5 s at 37 degrees C to 14 s at 25 degrees C. For the HCO3- dehydration reaction, pulmonary CA in situ displayed an apparent inhibition constant for ACTZ of 0.9-2.2 microM, a Michaelis-Menten constant of 90 mM, a maximal reaction velocity of 9 mM/s, and an apparent activation energy of 3.0 kcal/mol.


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E. Stabenau and T. Heming
CO2 excretion and postcapillary pH equilibration in blood-perfused turtle lungs
J. Exp. Biol., January 4, 1999; 202(8): 965 - 975.
[Abstract] [PDF]


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